1. Field of the Invention
This invention relates to an image forming apparatus which is capable of displaying image information such as characters and figures and obtaining such image information as a print. More particularly, it relates to an image forming apparatus in which image information is formed by toner on a repetitively usable image bearing member and such image information is used for display or printing.
2. Description of the Prior Art
To visualize signals used in communications or the like, there has heretofore been a printing apparatus of the electrophotographic type using a light beam modulated by such signals. This apparatus exposes the modulated light beam in the form of dots on the surface of a photosensitive member, instead of the image exposure by an original in a copying apparatus which is usually often used, and the epitome of such apparatus is shown in FIG. 1 of the acompanying drawings. Reference numeral 1 designates a photosensitive member having a photoconductive layer provided on a conductive substrate. The photosensitive member 1 is passed over pulleys P1 and P2 driven in the direction of arrows by a drive source, not shown. Reference numeral 2 denotes a charger, reference numeral 3 designates a transfer charger, reference numeral 4 denotes a scanner for scanning and exposing a modulated light beam on the photosensitive member 1, reference numeral 5 designates a lens, reference numeral 6 denotes a developing device, reference numeral 7 designates a discharging lamp for removing any residual charges, and reference numeral 8 denotes a cleaner for collecting any residual toner. The light beam reflected by the scanner 4 scans the surface of the photosensitive member, whereby an electrostatic latent image corresponsing to the signal information is formed on the photosensitive member 1.
The manner of scanning is shown in FIG. 2 of the accompanying drawings. In FIG. 2, reference numeral 11 designates a laser beam generator which generates a light beam modulated by signals. The light beam scans the surface of the photosensitive member 1 in a direction X substantially perpendicular to the direction of movement Z of the photosensitive member. In this case, the latent image formed on the surface of the photosensitive member is a mirror image of the image to be formed by transfer.
The above-described printing apparatus obtains the signal information as a hard copy only when the toner image in the form of a mirror image is transferred to a transfer material such as paper. However, for example, when the above-mentioned information need not be made into a hard copy, or when it is desired to know the substance of the signal information before it is made into a hard copy, it would occur to mind to use the apparatus as a display apparatus as shown in FIG. 3 of the accompanying drawings without making the apparatus into a printing apparatus. In FIG. 3, reference numeral 9 designates a transparent protecting portion such as transparent glass disposed in the display portion, and reference numeral 10 denotes an illuminating lamp for illuminating the photosensitive member 1 disposed in the display portion.
In this display apparatus, the image formed on the photosensitive member must be a positive image. Thus, if the light beam is scanned from right to left relative to the direction of movement of the photosensitive member as in the case of the printing apparatus of FIG. 2 and a latent image in the form of a mirror image is formed on the surface of the photosensitive member, in this display apparatus, the signal itself input to the light beam generator in said printing apparatus must be changed to form a latent image in the form of a positive image or the direction of rotation of the scanner 4 must be reversed and the light beam must be scanned from left to right toward the direction of movement of the photosensitive member, thereby forming a latent image in the form of a positive image.
An apparatus having the two functions of the above-described printing apparatus (FIG. 1) and the above-described display apparatus (FIG. 3) will now be considered. FIG. 4 of the accompanying drawings is a cross-sectional view showing an example of such apparatus. In FIG. 4, reference numeral 13 designates a fixing device for fixing the unfixed image on a transfer matereial, and reference numeral 12 designates a transfer material such as paper. Where this apparatus is used as a printing apparatus, transfer means such as transfer charger 3, the fixing device 13, etc. are operated and the scanner 4 scans the light beam in the direction of arrow indicated in FIG. 2. Where this apparatus is used as a display apparatus, the toner image on the photosensitive member 1 is not transferred to the transfer material and therefore, the various means for transfer are not operated and it is necessary to rotate the scanner 4 in a direction opposite to the direction of the arrows in FIG. 2 or to change the input signal itself of the light beam generator and make the latent image into a positive image.
Thus, in the method of making the latent image formed in the form of a mirror image into a positive image, as described above, it will be possible (1) to change the signal itself or (2) to reverse the direction of rotation of the scanner and in addition, (3) to change the direction of movement of the photosensitive member without changing the direction of rotation of the scanner.
However, in an image forming apparatus adopting the conventional latent image forming process, it is necessary that the developing device lie downstream of the latent image forming position as viewed in the direction of movement of the photosensitive member. Consequently, if the method of solution mentioned under item (3) above is adopted, latent image forming means and developing means must be disposed around the peripheral surface of the photosensitive member corresponding to the direction of movement of the photosensitive member. At the same time, the latent image forming means and the developing means must be selectively operated depending on the direction of movement of the photosensitive member, and this leads not only to a complicated construction but also to cumbersome control of operation and higher probability of malfunctioning or failure.